Surface-coated cutting tool and method for manufacturing the same

ABSTRACT

A surface-coated cutting tool has a rake face and a flank face, and includes a base material and a coating formed on the base material. The base material has a cutting edge face connecting the rake face to the flank face. The coating includes an aluminum oxide layer containing a plurality of aluminum oxide crystal grains. The aluminum oxide layer includes: a first region made up of a region A on the rake face and a region B on the flank face; a second region on the rake face except for the region A; and a third region on the flank face except for the region B. The aluminum oxide layer satisfies a relation: b−a&gt;0.5, where a is an average value of TC(006) in the first region in texture coefficient TC(hkl), and b is an average value of TC(006) in the second or third region in texture coefficient TC(hkl).

TECHNICAL FIELD

The present invention relates to a surface-coated cutting tool and amethod for manufacturing the surface-coated cutting tool. The presentapplication claims priority to Japanese Patent Application No.2016-164783 filed on Aug. 25, 2016, the disclosure of which is herebyincorporated by reference in its entirety.

BACKGROUND ART

Various techniques have been proposed with the aim of improving theperformance of a surface-coated cutting tool, such as a technique forimproving the quality of the coating by varying the texture coefficientsof Al₂O₃. For example, Japanese Patent No. 5904389 (PTL 1) discloses asurface-coated cutting tool including a base material and a coating onthe base material. In the coating, TC(006) in texture coefficientTC(hkl) in the vicinity of the cutting edge is made lower than that inthe remaining region to thereby suppress sudden chipping of the cuttingedge while maintaining a high thermal conductivity.

Japanese Patent Laying-Open No. 2012-213853 (PTL 2) discloses a coatedcutting tool insert produced by forming a coating layer on a basematerial and performing a surface treatment on the coating layer. Theinsert has wear resistance and toughness improved by controlling thediffraction intensity ratio I(012)/I(024) under x-ray diffractometry.

CITATION LIST Patent Literature

PTL 1: Japanese Patent No. 5904389

PTL 2: Japanese Patent Laying-Open No. 2012-213853

SUMMARY OF INVENTION

A surface-coated cutting tool according to an aspect of the presentdisclosure is a surface-coated cutting tool having a rake face and aflank face. The surface-coated cutting tool includes a base material anda coating formed on the base material. The base material is a cementedcarbide or a cermet. The base material has a surface, and the surfaceincludes the rake face, the flank face, and a cutting edge faceconnecting the rake face to the flank face. The base material has anoxygen concentration of less than or equal to 1 at. % at a depthposition of 0.4 μm from the cutting edge face. The coating includes analuminum oxide layer containing a plurality of aluminum oxide crystalgrains. The aluminum oxide layer includes: a first region made up of aregion A on the rake face and a region B on the flank face; a secondregion on the rake face except for the region A; and a third region onthe flank face except for the region B. The region A is a region from anedge ridgeline to an imaginary line on the rake face, wherein the edgeridgeline is a line at which an imaginary extension of the rake face andan imaginary extension of the flank face cross each other, and theimaginary line on the rake face is a line extending along the edgeridgeline and located 1 mm away from the edge ridgeline. The region B isa region from the edge ridgeline to an imaginary line on the flank face,wherein the imaginary line on the flank face is a line extending alongthe edge ridgeline and located 1 mm away from the edge ridgeline. Thealuminum oxide layer satisfies a relation: b−a>0.5, where a is anaverage value of a TC(006) in the first region in texture coefficientTC(hkl), and b is an average value of the TC(006) in the second regionor the third region in texture coefficient TC(hkl).

A method for manufacturing a surface-coated cutting tool according to anaspect of the present disclosure is a method for manufacturing theabove-described surface-coated cutting tool. The method includes:preparing a base material precursor; preparing the base material bymachining a surface of the base material precursor to form the cuttingedge face; forming the coating on the base material; and performing asurface treatment on a portion of the coating, the portion correspondingto the first region.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is an explanatory diagram schematically showing measurementpoints at five locations on a surface-coated cutting tool to beirradiated with x-ray for calculating TC(hkl) by x-ray diffractometry.

FIG. 2 is a perspective view showing an example of a base material.

FIG. 3 is a cross-sectional view along line X-X as seen in the directionindicated by arrows in FIG. 2.

FIG. 4 is a partially enlarged view of FIG. 3.

FIG. 5 is an explanatory diagram schematically showing the direction(angle) in which blast is applied to a portion corresponding to a firstregion of a coating during surface treatment.

DETAILED DESCRIPTION Problem to be Solved by the Present Disclosure

As for the surface-coated cutting tool of PTL 1, however, the adhesionbetween the base material and the coating, specifically the function ofpreventing peel-off of the coating during cutting, for example, leaves aroom for improvement. The cutting tool of PTL 2 is insufficient inchipping resistance.

In view of the above, an object of the present disclosure is to providea surface-coated cutting tool having improved resistance to coatingfracture including peel-off and chipping, for example (hereinafter alsoreferred to as “fracture resistance”) while maintaining a high wearresistance, as well as a method for manufacturing the surface-coatedcutting tool.

Advantageous Effect of the Present Disclosure

According to the foregoing, there is provided a surface-coated cuttingtool with improved resistance to coating fracture including peel-off andchipping, for example, while maintaining a high wear resistance.

Description of Embodiments

First of all, the present invention is described based on aspects listedbelow.

[1] A surface-coated cutting tool according to an aspect of the presentdisclosure is a surface-coated cutting tool having a rake face and aflank face. The surface-coated cutting tool includes a base material anda coating formed on the base material. The base material is a cementedcarbide or a cermet. The base material has a surface, and the surfaceincludes the rake face, the flank face, and a cutting edge faceconnecting the rake face to the flank face. The base material has anoxygen concentration of less than or equal to 1 at. % at a depthposition of 0.4 μm from the cutting edge face. The coating includes analuminum oxide layer containing a plurality of aluminum oxide crystalgrains. The aluminum oxide layer includes: a first region made up of aregion A on the rake face and a region B on the flank face; a secondregion on the rake face except for the region A; and a third region onthe flank face except for the region B. The region A is a region from anedge ridgeline to an imaginary line on the rake face, wherein the edgeridgeline is a line at which an imaginary extension of the rake face andan imaginary extension of the flank face cross each other, and theimaginary line on the rake face is a line extending along the edgeridgeline and located 1 mm away from the edge ridgeline. The region B isa region from the edge ridgeline to an imaginary line on the flank face,wherein the imaginary line on the flank face is a line extending alongthe edge ridgeline and located 1 mm away from the edge ridgeline. Thealuminum oxide layer satisfies a relation: b−a>0.5, where a is anaverage value of a TC(006) in the first region in texture coefficientTC(hkl), and b is an average value of the TC(006) in the second regionor the third region in texture coefficient TC(hkl). These featuresenable the surface-coated cutting tool to have increased resistance tocoating fracture including peel-off and chipping for example, whilemaintaining a high wear resistance.

Preferably, the a satisfies a relation: 4<a. Accordingly, the resistanceto coating fracture including peel-off and chipping for example canfurther be increased.

Preferably, the aluminum oxide layer is an α-Al₂O₃ layer containingα-Al₂O₃ crystal grains as a main component. Accordingly, the resistanceto coating fracture including peel-off and chipping for example canfurther be increased.

Preferably, the base material has an oxygen concentration of less thanor equal to 10 at. % at a depth position of 0.2 μm from the cutting edgeface. Accordingly, the adhesiveness between the base material and thecoating can further be improved.

Preferably, the cutting edge face has a strain of less than or equal to0.07. Accordingly, the adhesiveness between the base material and thecoating can be improved as well.

Preferably, the cemented carbide has a composition made up of 5 to 7mass % of cobalt, 0.01 to 3 mass % of a carbide of a first metal, andthe balance of tungsten carbide and inevitable impurities. The cermethas a composition made up of 5 to 25 mass % of cobalt or nickel, 5 to 40mass % of tungsten carbide, and the balance of inevitable impurities andat least one selected from a carbide of the first metal, a nitride ofthe first metal, and a carbonitride of the first metal. The first metalis preferably at least one kind of metal selected from the groupconsisting of Group IV elements, Group V elements, and Group VI elementsin the periodic table. Accordingly, a base material made of a cementedcarbide or a cermet can be included that is excellent in balance betweenhardness and strength at high temperature.

Preferably, the coating further includes a compound layer made from: atleast one kind of first element selected from the group consisting ofGroup IV elements, Group V elements, and Group VI elements in theperiodic table, aluminum, and silicon; and at least one kind of secondelement selected from the group consisting of boron, carbon, nitrogen,and oxygen. Accordingly, the quality of the coating can be improved.

Preferably, the coating is a chemical vapor deposition film.Accordingly, the adhesiveness between the base material and the coatingcan be improved as well.

A method for manufacturing a surface-coated cutting tool according to anaspect of the present disclosure is a method for manufacturing theabove-described surface-coated cutting tool. The method includes:preparing a base material precursor; preparing the base material bymachining a surface of the base material precursor to form the cuttingedge face; forming the coating on the base material; and performing asurface treatment on a portion of the coating, the portion correspondingto the first region. Accordingly, a surface-coated cutting tool can bemanufactured having increased resistance to coating fracture includingpeel-off and chipping for example, while maintaining a high wearresistance.

Preferably, the machining is one of a first grinding process ofalternately repeating wet grinding and dry grinding, a second grindingprocess of performing low- feed low-depth-of-cut wet grinding, or athird grinding process of performing dry grinding. Accordingly, asurface-coated cutting tool having increased resistance to coatingfracture including peel-off and chipping for example can bemanufactured.

Preferably, the surface treatment includes at least brushing orblasting. Accordingly, a surface-coated cutting tool having furtherimproved fracture resistance can be manufactured.

Details of Embodiments of the Invention

In the following, an embodiment (hereinafter also referred to as“present embodiment”) of the present invention is described in furtherdetail. In the drawings used for the following description of theembodiment, the same reference characters denote the same parts orcorresponding parts.

The expression “A to B” as used herein is intended to define an upperlimit and a lower limit of a certain range (i.e., from A to Binclusive). As to “A to B” where A is not followed by a unit symbol andonly B is followed by a unit symbol, the unit of A is the same as theunit of B. Further, a compound or the like expressed herein by achemical formula includes the compound with any of all conventionallyknown atomic ratios if the atomic ratio is not particularly limited, andthe compound is not necessarily limited to the compound with astoichiometric ratio. For example, in the case of an expression “TiAlN,”the ratio of the number of atoms between the elements constituting TiAlNis not limited to Ti:Al:N=0.5:0.5:1, and includes all conventionallyknown ratios of the number of atoms. This is applied as well to anyexpressions of compounds other than “TiAlN.” In the present embodiment,the metal element such as titanium (Ti), aluminum (Al), silicon (Si),tantalum (Ta), chromium (Cr) and the non-metal element such as nitrogen(N), oxygen (O), or carbon (C) may not necessarily constitute astoichiometric composition.

<<Surface-Coated Cutting Tool>>

A surface-coated cutting tool according to the present embodiment has arake face and a flank face. The rake face of the surface-coated cuttingtool is chiefly a surface which is in contact with swarf of a workpieceduring cutting. For example, in the explanatory diagram of FIG. 1, thetop surface and the bottom surface of the surface-coated cutting toolare each a rake face. The flank face is chiefly a surface which faces aprocessed surface (a surface newly formed by cutting the workpiece). Forexample, in the explanatory diagram of FIG. 1, the flank face is theside surface of the surface-coated cutting tool. In the presentembodiment, the boundary between the rake face and the flank faceundergoes a surface treatment as described later herein to form a tooledge portion. The tool edge portion is usually a portion serving as acutting edge (hereinafter also referred to simply as “edge”) of thesurface-coated cutting tool.

The shape of the tool edge portion may be any of a sharp edge (ridge atwhich the rake face and the flank face meet each other), a honed edge(sharp edge processed to be rounded), a negative land (beveled), acombination of the honed edge and the negative land, and the like. Thetool edge portion which undergoes a surface treatment into a honed edgehas an arcuate surface. The tool edge portion which undergoes a surfacetreatment into a negative land shape has a beveled surface. The tooledge portion which undergoes a surface treatment into a sharp edge shapehas a ridgeline which is the boundary between the rake face and theflank face.

In order to determine the range of a below-described first region (aregion A and a region B) for example, a line (also referred to as “edgeridgeline” hereinafter) at which respective imaginary extensions of therake face and the flank face of the surface-coated cutting tool crosseach other is herein necessary. This line corresponds to a ridgelineformed by a surface treatment of the tool edge portion into a sharpedge. This line is not present if a surface treatment is performed toform a honed edge or a negative land shape, because this line isreplaced with the tool edge portion. In these cases as well, thefollowing description is given in which the surface-coated cutting toolis regarded as having an imaginary edge ridgeline, in order to determinethe range of the below-described first region (region A and region B)for example.

The surface-coated cutting tool includes a base material and a coatingformed on the base material. The coating preferably covers the entiresurface of the base material. However, even when a part of the basematerial is not covered with the coating or the makeup of the coating ispartially different, such a surface-coated cutting tool does not gobeyond the scope of the present invention.

The surface-coated cutting tool can suitably be used as a cutting toolsuch as drill, end mill, indexable insert for the drill, indexableinsert for the end mill, indexable insert for milling, indexable insertfor turning, metal-slitting saw, gear-cutting tool, reamer, tap, or thelike. In the case where the surface-coated cutting tool is an indexableinsert, the base material may have or may not have a chip breaker.

<Coating>

The coating includes an aluminum oxide layer containing a plurality ofaluminum oxide (also expressed as “Al₂O₃” hereinafter) crystal grains(polycrystal).

In the present embodiment, the aluminum oxide layer is a layercontaining at least Al₂O₃ as a part of the layer (a layer containingmore than or equal to 50 mass % of Al₂O₃ is regarded as an Al₂O₃ layer),and may contain ZrO₂, Y₂O₃ (may also be regarded as a layer in which Zror Y is be added to Al₂O₃), or the like. The aluminum oxide layer mayfurther contain impurities such as chlorine, carbon, boron, nitrogen,and the like. The Al₂O₃ layer may alternatively be made up of Al₂O₃ andimpurities only. The crystal structure of Al₂O₃ contained in the Al₂O₃layer should not be limited to a particular crystal structure. Forexample, Al₂O₃ may be α-Al₂O₃ (aluminum oxide having α-type crystalstructure), κ-Al₂O₃ (aluminum oxide having κ-type crystal structure),γ-Al₂O₃ (aluminum oxide having γ-type crystal structure), amorphousAl₂O₃, or a mixture thereof. In the following description, theillustrated aluminum oxide layer is an α-Al₂O₃ layer containing α-Al₂O₃crystal grains as a main component.

“Containing α-Al₂O₃ crystal grains as a main component” means that theα-Al₂O₃ crystal grains occupy 90 mass % or more of Al₂O₃ crystal grainsconstituting the aluminum oxide layer. Preferably, “containing α-Al₂O₃crystal grains as a main component” also means that the α-Al₂O₃ layerconsists of the α-Al₂O₃ crystal grains except for the case where crystalgrains of at least one of y-Al₂O₃ and κ-Al₂O₃ are inevitably contained.

The ratio of α-Al₂O₃ crystal grains to the Al₂O₃ crystal grainsconstituting the aluminum oxide layer can be measured by analyzingdiffraction peaks by means of an x-ray diffractometer.

First Region, Second Region, and Third Region

The α-Al₂O₃ layer (aluminum oxide layer) includes a first region made upof a region A on the rake face and a region B on the flank face. Theα-Al₂O₃ layer further includes a second region on the rake face exceptfor the region A. The α-Al₂O₃ layer also includes a third region on theflank face except for the region B. The region A is a region from anedge ridgeline to an imaginary line on the rake face. The edge ridgelineis a line at which an imaginary extension of the rake face and animaginary extension of the flank face cross each other. The imaginaryline on the rake face is a line extending along the edge ridgeline andlocated 1 mm away from the edge ridgeline. The region B is a region fromthe edge ridgeline to an imaginary line on the flank face. The imaginaryline on the flank face is a line extending along the edge ridgeline andlocated 1 mm away from the edge ridgeline. The first region thereforeincludes the edge ridgeline, and also includes a point of intersection(also referred to as “corner” hereinafter) of edge ridgelines, a pointof intersection of the imaginary lines, and the point of intersection ofthe edge ridgeline and the imaginary line. The second region and thethird region do not include the edge ridgeline.

TC(006) in First Region and Second Region

The α-Al₂O₃ layer (aluminum oxide layer) satisfies a relation b−a>0.5where a is an average value of TC(006) in the first region in texturecoefficient TC(hkl) and b is an average value of TC(006) in the secondregion in texture coefficient TC(hkl). Accordingly, the (001)orientation is controlled to be relatively low in the cutting edgeportion only, while the wear resistance based on high (001) orientationin the α-Al₂O₃ layer is maintained, and thereby sudden chipping of thecutting edge can be suppressed.

TC(006) in Third Region

The second region is formed in the rake face. In some cases, it may bedifficult to measure the texture coefficient TC(hkl) due to unevennessof the rake face.

In such a case as well, the α-Al₂O₃ layer (aluminum oxide layer)satisfies a relation b−a>0.5, where b is an average value of TC(006) inthe third region and a is an average value of TC(006) in the firstregion. Accordingly, the (001) orientation is controlled to berelatively low in the cutting edge portion only, while a high wearresistance based on the high (001) orientation in the α-Al₂O₃ layer ismaintained, and thereby sudden chipping of the cutting edge can besuppressed.

The “(001) orientation” in the α-Al₂O₃ layer means that the (006) planeis a reflection plane exhibiting the highest numerical value of texturecoefficient TC(hkl) among (hkl) reflection planes (eight reflectionplanes in the present embodiment described later herein) in an α-Al₂O₃layer diffraction profile obtained through analysis by means of an x-raydiffractometer described later herein. Texture coefficient TC(hkl) canbe defined by the following expression (1).

$\begin{matrix}{{{TC}({hkl})} = {\frac{I({hkl})}{I_{0}({hkl})}\left\{ {\frac{1}{n}{\sum_{1}^{n}\frac{I({hkl})}{I_{0}({hkl})}}} \right\}^{- 1}}} & (1)\end{matrix}$

In the expression (1), I(hkl) represents an x-ray diffraction intensityof a (hkl) reflection plane, and I₀(hkl) represents a standard intensityaccording to PDF card No. 00-042-1468 of the ICDD. In the expression(1), n represents the number of reflections used for the calculation. As(hkl) reflections, (012), (104), (110), (006), (113), (024), (116), and(300) are used. Therefore, n is eight in the present embodiment.

ICDD (registered trademark) is an abbreviation for International Centerfor Diffraction Data. PDF (registered trademark) is an abbreviation forPower Diffraction File.

TC(006) measured at any locations in the first region, the secondregion, and the third region of the α-Al₂O₃ layer can be expressed bythe following expression (2).

$\begin{matrix}{{{TC}(006)} = {\frac{I(006)}{I_{0}(006)}\left\{ {\frac{1}{8}{\sum_{1}^{8}\frac{I({hkl})}{I_{0}({hkl})}}} \right\}^{- 1}}} & (2)\end{matrix}$

This TC(hkl) can be measured through analysis by means of an x-raydiffractometer. TC(hkl) can for example be measured by means of an x-raydiffractometer (trade name: “SmartLab (registered trademark) 3”manufactured by Rigaku Corporation) under the following conditions.

characteristic x-ray: Cu-Kα

tube voltage: 45 kV

tube current: 200 mA

x-ray diffractometry: 0-20 method

range of x-ray irradiation: A pinhole collimator is used to irradiate arange on the order of 0.3 mm in diameter with x-ray.

In the present embodiment, TC(006) is measured for example in the rakeface of the surface-coated cutting tool. As long as it is measured inthe rake face of the surface-coated cutting tool, a plurality ofmeasurement points for measuring TC(006) can be set at anynon-overlapping locations in the first region (region A), and similarlya plurality of measurement points can be set at any non-overlappinglocations in the second region. The measurement points are irradiatedwith x-ray to obtain the values of TC(006). The values of a and b whichare averages of these values can thus be calculated.

If it is difficult to measure texture coefficient TC(hkl) due tounevenness of the rake face, TC(006) may be measured in the flank faceof the surface-coated cutting tool. In this case as well, a plurality ofmeasurement points for measuring TC(006) can be set at anynon-overlapping locations in the first region (region B) of the flankface, and similarly a plurality of measurement points can be set at anynon-overlapping locations in the third region. The measurement pointsare irradiated with x-ray to obtain TC(006). The values of a and b whichare averages of these values can thus be calculated.

Preferably, the measurement points are set by selecting flat portions onthe first region, the second region, and the third region. Preferably,the measurement points are two or more non-overlapping points asdescribed above. However, in such a case where measurement points to beset are inevitably overlapping on the first region, the second region,or the third region, only one measurement point may be set. If TC(006)at a measurement point is apparently an abnormal value, the abnormalvalue should be excluded.

In the present embodiment, as shown in FIG. 1 for example, measurementpoints (first measurement point 1, second measurement point 2, thirdmeasurement point 3, fourth measurement point 4, fifth measurement point5) may be set at intervals of 0.7 mm from a corner 100 (corner which isa point of intersection of two edge ridgelines) along the diagonal lineconnecting corner 100 and a corner 200 each having an acute angle(θ=80°), out of the four vertexes formed by extending the rake face andthe flank face. These measurement points are irradiated with x-ray underthe above-described conditions to obtain data from x-ray diffraction(XRD) (also referred to as “diffraction profile” hereinafter) in theα-Al₂O₃ layer. Based on the diffraction profile in the α-Al₂O₃ layer,TC(006) can be calculated.

The first region is made up of: the region from the edge ridgeline to animaginary line on the rake face, the imaginary line being located 1 mmaway from the edge ridgeline and extending along the edge ridgeline(region A); and the region from the edge ridgeline to an imaginary lineon the flank face, the imaginary line being located 1 mm away from theedge ridgeline and extending along the edge ridgeline (region B). Theedge ridgeline itself is also included in the first region. Therefore,based on FIG. 1, first measurement point 1 and second measurement point2 which are set at intervals of 0.7 mm from the corner along thediagonal line connecting corners 100 and 200 of an acute angle (θ=80°)are included in the first region. The average of the values of TC(006)measured at these measurement points is the value of a.

The second region is a region of the rake face except for region A.Therefore, third measurement point 3, fourth measurement point 4, andfifth measurement point 5 which are set at intervals of 0.7 mm along theaforementioned diagonal line subsequently to first measurement point 1and second measurement point 2 are included in the second region. Theaverage of the values of TC(006) measured at these measurement points isthe value of b. In the present embodiment, a value of b−a calculatedbased on a and b is more than 0.5. As to the upper limit of b−a, arelation b−a<8 is met, since the upper limit of TC(006) is 8 based onthe definition of the above expression (1).

In FIG. 1, the measurement points are set on the diagonal line extendingfrom the corner of the surface-coated cutting tool toward the centerthereof. The present embodiment, however, should not be limited to this.For example, in each of the first region, the second region, and thethird region, a plurality of measurement points can be distributed asmuch as possible, and TC(006) can be measured at these measurementpoints.

For example, measurement points in the first region may be set at onepoint or two or more points on an intermediate line between the edgeridgeline and an imaginary line extending along the edge ridgeline andlocated 1 mm away from the edge ridgeline. Measurement points in thesecond region may be set at one point or two or more points on a linelocated 1 mm away toward the second region from the boundary between thefirst region and the second region (i.e., the imaginary line on the rakeface extending along the edge ridgeline and located 1 mm away from theedge ridgeline). Further, measurement points in the third region may beset at one point or two or more points on a line located 1 mm awaytoward the third region from the boundary between the first region andthe third region (the imaginary line on the flank face extending alongthe edge ridgeline and located 1 mm away from the edge ridgeline).Besides, for a surface-coated cutting tool in the shape of a regularpolygon having four or more sides, the measurement points can be set onthe diagonal line similarly to the example shown in FIG. 1. If thesurface-coated cutting tool is circular in shape, the measurement pointscan be set at one given point on the edge ridgeline and one point or twoor more points on a line passing through the center of the circle.

Average value a of TC(006) in the first region preferably satisfies arelation 4<a. Average value b of TC(006) in the second region or thirdregion preferably satisfies a relation 5<b. The upper limit of a is 7.4,and the upper limit of b is 8. When these relations are satisfied, theheight of the (001) orientation can be controlled to be relatively lowin the cutting edge portion only, while maintaining a high wearresistance based on the high (001) orientation in the α-Al₂O₃ layer.Accordingly, sudden chipping of the cutting edge can be suppressed.

When a meets a relation a≤4, the orientation in a specific direction[(001) orientation] in the first region of the α-Al₂O₃ layer (aluminumoxide layer) may be excessively low and the α-Al₂O₃ layer may not havethe (001) orientation. In such a case, there is a possibility that thecoating in the first region cannot have desired hardness and strength.When a meets a relation 7.4<a, the orientation in a specific direction[(001) orientation] is excessively high in the first region of theα-Al₂O₃ layer and there is a possibility that sudden chipping of thecutting edge is prone to occur.

In the case where b meets a relation b≤5, the orientation in a specificdirection [(001) orientation] is excessively low in the α-Al₂O₃ layeracross the whole tool and there is a possibility that the α-Al₂O₃ layermay not have the (001) orientation. In such a case, there is apossibility that a high wear resistance of the α-Al₂O₃ crystal grainscannot be maintained in the whole tool.

Other Layers

The coating may have a single layer structure made up of a singlealuminum oxide layer as described above, or a multilayer structure madeup of a stack of two or more layers consisting of the aluminum oxidelayer and another layer/other layers. The coating may be formed on apart (cutting edge face for example) of the surface of the base materialas described above, or the entire surface of the base material.

In the case of the coating having the multilayer structure made up of astack of two or more layers, preferably the coating further includes thealuminum oxide layer as described above and a compound layer (alsoreferred to as “other layer(s)” hereinafter) made from: at least onekind of first element selected from the group consisting of Group IVelements (such as Ti, Zr, Hf), Group V elements (such as V, Nb, Ta), andGroup VI elements (such as Cr, Mo, W) in the periodic table; and atleast one kind of second element selected from the group consisting ofboron, carbon, nitrogen, and oxygen. Accordingly, the adhesivenessbetween the base material and the coating can further be improved, andthis coating is suitable as a coating of the surface-coated cuttingtool. It should be noted that the other layer made of a combination ofaluminum as a first element and oxygen as a second element is excluded,because this combination forms an aluminum oxide layer.

Specific examples of the compound layer (other layers) may be TiCNOlayer, TiBN layer, TiC layer, TiN layer, TiAlN layer, TiSiN layer, AlCrNlayer, TiAlSiN layer, TiAlNO layer, AlCrSiCN layer, TiCN layer, TiSiClayer, CrSiN layer, AlTiSiCO layer, TiSiCN layer, ZrO₂ layer, and thelike. The compound layer is preferably a layer containing Ti (e.g. TiCNlayer, TiN layer) since such a layer is particularly excellent inhardness, or preferably a layer containing Al (e.g. AlCrN layer) sincesuch a layer is particularly excellent in oxidation resistance.

The TiCN layer as an example of the other layers is preferably locatedbetween the Al₂O₃ layer and the base material. The TiCN layer having ahigh wear resistance can impart a still more suitable wear resistance tothe coating. The TiCN layer is particularly preferably formed by theMT-CVD (medium temperature CVD) method. The MT-CVD method enables filmsto be deposited at a relatively low temperature of about 850 to 900° C.,which can reduce damages to the base material due to heating during thefilm deposition.

The coating may further include, as still other layers, a topmost layerand an intermediate layer, for example. The topmost layer is a layerlocated uppermost in the coating. The intermediate layer is a layerlocated between the topmost layer and the α-Al₂O₃ layer, between theα-Al₂O₃ layer and the TiCN layer, or between the TiCN layer and the basematerial, for example. The topmost layer may be a TiN layer, forexample. The intermediate layer may be a TiCNO layer, for example.

In the present embodiment, preferably the coating is a chemical vapordeposition layer. Specifically, it is suitable to form the coating onthe base material by the chemical vapor deposition (CVD) method asdescribed later herein. The film deposition temperature of the CVDmethod is 800 to 1200° C. which is higher than that of the physicalvapor deposition method. The CVD method thus provides an advantageouseffect that the adhesiveness between the base material and the coatingis improved, as compared with the physical vapor deposition method.

Preferably, the coating has a thickness of 0.3 to 25 μm. The coatinghaving a thickness of 0.3 μm or more can sufficiently exhibit thecharacteristics of the coating. The coating having a thickness of 25 μmor less can suppress peel-off of the coating due to an excessively largethickness of the coating.

Each of respective thicknesses of the coating, the α-Al₂O₃ layer(aluminum oxide layer), and the other layer(s) is herein an averagethickness. These thicknesses can be measured with a field emissionscanning electron microscopy (FE-SEM) in accordance with the followingmethod.

First, the surface-coated cutting tool is cut along a plane which isparallel with a normal line to the rake face of the surface-coatedcutting tool so as to expose a cross section thereof. Subsequently, theexposed cross section is polished to produce a polished surface to beobserved. When the thickness of the coating is measured, observation ata magnification of 5000× is carried out for five given sites (fivefields of view) including the coating appearing on this polished surfaceto be observed, so as to determine the thickness of the coating.Finally, the average value of respective values of the five fields ofview is determined, and the determined average value is identified asthe average thickness of the coating. When respective thicknesses of theα-Al₂O₃ layer and the other layer(s) are measured, observation at amagnification of 5000× is carried out for five given sites (five fieldsof view) including the α-Al₂O₃ layer and the other layer(s) appearing onthe polished surface to be observed, so as to determine each thickness.Finally, the average value of respective values of the five fields ofview is determined, and the determined average value is identified asthe average thickness of each of the α-Al₂O₃ layer and the otherlayer(s).

The cross section of the base material covered with the coating may bepolished by a conventionally known method. For example, the crosssection of the base material may undergo ion milling using argon (Ar)ions to obtain a smoothed polished surface to be observed. Theconditions for the ion milling with Ar ions are for example as follows.

accelerated voltage: 6 kV

ion beam angle: 0 to 5° from a normal line to the rake face of the basematerial

ion beam application time: 6 hours

The smoothed polished surface to be observed may thereafter be analyzedby means of an FE-SEM.

<Base Material>

The base material has a surface. The surface includes a rake face, aflank face, and a cutting edge face connecting the rake face to theflank face. Specifically, the rake face included in the surface of thebase material is a surface on the base material corresponding to therake face of the surface-coated cutting tool. The flank face included inthe surface of the base material is a surface on the base materialcorresponding to the flank face of the surface-coated cutting tool. Thecutting edge face included in the surface of the base material is theone as described above. The cutting edge face may have an arcuatesurface shape, a planar surface shape, a shape of a combination of aplaner surface and an arcuate surface, or a sharp edge shape, asdescribed below. Specifically, the cutting edge face included in thesurface of the base material is a surface on the base materialcorresponding to the tool edge portion of the surface-coated cuttingtool. The cutting edge face included in the base material is furtherdescribed below with reference to FIGS. 2 to 4.

FIG. 2 is a perspective view showing an example of the base material.FIG. 3 is a cross-sectional view along line X-X as seen in the directionindicated by arrows in FIG. 2. The base material in such a shape is usedas a base material of an indexable insert for turning, for example.

A base material 10 shown in FIGS. 2 and 3 has a surface including anupper surface, a lower surface, and four side surfaces. The overallshape of base material 10 shown in FIGS. 2 and 3 is a quadrangular prismwhich is flat in the left-to-right direction in FIGS. 2 and 3. Basematerial 10 has a through hole extending through the upper and lowersurfaces. Of the four side surfaces, side surfaces adjacent to eachother are connected to each other by an arcuate surface along theboundary between these side surfaces.

The top surface and the bottom surface of base material 10 are rakefaces 10 a, the four side surfaces thereof (and the arcuate surfaceseach connecting the side surfaces to each other) are flank faces 10 b,and an arcuate surface connecting rake face 10 a to flank face 10 b is acutting edge face 10 c.

FIG. 4 is a partially enlarged view of FIG. 3. FIG. 4 shows an imaginaryplane A including rake face 10 a, an imaginary boundary line AA at whichrake face 10 a and imaginary plane A part from each other, an imaginaryplane B including flank face 10 b, and an imaginary boundary line BB atwhich flank face 10 b and imaginary plane B part from each other. InFIG. 4, each imaginary plane A, B is shown as a line and each imaginaryboundary line AA, BB is shown as a dot. In FIG. 4, the surface withinthe region from imaginary boundary line AA to imaginary boundary line BBis cutting edge face 10 c.

Cutting edge face 10 c is a surface of base material 10. The ridgelineat which surfaces of base material 10 meet is machined to form cuttingedge face 10 c. Specifically, at least a part of the surface of a basematerial precursor made from a sintered material or the like is machinedto form base material 10, and the surface of base material 10 is beveledby machining to form a surface called cutting edge face 10 c.

FIGS. 2 to 4 show cutting edge face 10 c in the shape of an arcuatesurface (so-called honed edge). The shape of the cutting edge face,however, should not be limited to this. For example, the shape of thecutting edge face may be a planar surface (so-called negative land), acombination of a planar surface and an arcuate surface (so-called acombination of honed edge and negative land), or a sharp edge (ridge atwhich the rake face and the flank face meet each other).

In the case of the cutting edge face in the shape of a sharp edge, it isdifficult to determine, based on the shape of the sharp edge, theboundary between the cutting edge face formed by machining and the rakeface/flank face. Therefore, in the case of the base material having theshape of a sharp edge, the surface included in the region extending to adistance of 30 μm from the ridgeline at which the rake face and theflank face meet each other is herein identified as the cutting edgeface, because this region can serve as a cutting edge of thesurface-coated cutting tool.

Oxygen Concentration

The base material has an oxygen concentration of less than or equal to 1at. % at a depth position of 0.4 μm from the cutting edge face. Theoxygen concentration can be measured with an XPS (X-ray PhotoelectronSpectroscopy) analyzer to which XPS can be applied.

The XPS analyzer can be used to measure the ratio of atoms of a givenkind (element distribution) at a given depth position in a target ofmeasurement while etching the surface of the target by means of ions ofAr for example. XPS can thus be applied to determine the oxygenconcentration at a depth position of 0.4 μm from the cutting edge faceof the base material. The etching area may be 5000 to 50000 μm². Theoxygen concentration is measured under vacuum.

Regarding the cutting edge face having a sharp edge shape, the cuttingedge face includes a cutting edge face on the rake face side and acutting edge face on the flank face side. In this case, “a depthposition of 0.4 μm from the cutting edge face which is a surface of thebase material” means a position at a depth of 0.4 μm from one of thecutting edge faces on the rake face side and the flank face side and ata depth of more than or equal to 0.4 μm from the other cutting edgeface.

In the present embodiment, the coating is formed on the surface of thebase material, and therefore, the surface of the base material isdetermined in the following way. First, XPS is used to etch the coatingin the depth direction by ions of Ar for example, from the topmostsurface of the surface-coated cutting tool corresponding to the cuttingedge face of the base material. Next, the depth position at which anelement specific to the raw material for the base material (e.g. anelement forming a binder phase in the base material and may be Co, forexample) is measured is identified as a cutting edge face of the basematerial.

The oxygen concentration may be an average value. Specifically, giventhree measurement sites are determined on the cutting edge face of thebase material, and the oxygen concentration is measured at a depthposition of 0.4 μm from each of the measurement sites. The average ofrespective oxygen concentrations measured at these sites may bedetermined as the oxygen concentration.

The inventors of the present invention measured the oxygen concentrationat a plurality of measurement sites of the cutting edge face to findthat there is no significant difference between the value taken at eachmeasurement site and the average value. Therefore, the oxygenconcentration may be measured at a given single site of the cutting edgeface and the value taken at this site may be determined as the oxygenconcentration. If the measured oxygen concentration has an apparentlyabnormal value, however, such a value should be excluded. The singlesite is preferably determined in a central portion of the cutting edgeface, since this portion contributes significantly to characteristics ofthe cutting tool and is therefore appropriate as a site for evaluatingthe characteristics of the cutting tool.

In the surface-coated cutting tool of the present embodiment, the basematerial may have an oxygen concentration of less than or equal to 1 at.% at a depth position of 0.4 μm from the cutting edge face to therebyimpart a high fracture resistance and accordingly a long life to thesurface-coated cutting tool.

The inventors have found the following (a) to (c) by studies regardingthe present disclosure:

(a) in the cutting edge face of the base material for the surface-coatedcutting tool, unintended oxygen atoms have entered, and the oxygenconcentration derived from the oxygen atoms is highest in the vicinityof the cutting edge face and decreases gradually toward the inside ofthe base material;

(b) the higher the oxygen concentration in the vicinity of the cuttingedge face, oxygen atoms tend to enter deeper in the base material;

(c) in the base material in which oxygen atoms enter deep from thecutting edge face, cracks are likely to extend inward from the cuttingedge face and hard particles forming the base material are likely todrop off

Based on the above findings, the inventors suppose the reasons why thesurface-coated cutting tool of the present disclosure has the highfracture resistance. Specifically, in the base material of theconventional surface-coated cutting tool, unintended oxygen atoms arepresent in a region from the cutting edge face inward to a certain depthposition. In a region in which the oxygen atoms are present at a highconcentration that may influence the physical properties of the basematerial (“high oxygen region”), the base material embrittles. Cracksgenerated in the cutting edge face are therefore likely to extend withinthe high oxygen region extending from the cutting edge face inward (inthe depth direction of the base material).

Further, in the conventional surface-coated cutting tool, the highoxygen region has a relatively large width (the depth extending straightfrom the cutting edge face toward the inside of the base material).Consequently, large (long) cracks are generated. Accordingly, hardparticles included in the high oxygen region and hard particles mostlylocated in the high oxygen region are likely to drop off

In contrast, the base material of the present disclosure has an oxygenconcentration of less than or equal to 1 at. % at a depth position of0.4 μm from the cutting edge face, and the width of the high oxygenregion is smaller than that of the conventional cutting tool or the basematerial does not have a high oxygen region. Therefore, the region inwhich brittlement may occur is smaller than the conventional cuttingtool or there is no such a region, which provides higher hardness thanthe conventional cutting tool. Further, even when an origin of a crackis generated, extension of the crack is reduced as compared with theconventional cutting tool.

In particular, when the oxygen concentration at a depth position of 0.4μm is less than or equal to 1 at. %, the width of the high oxygen regionis likely to be smaller than the particle size of hard particles locatedin the surface of the base material. Therefore, even when cracks extendacross the entire high oxygen region, the length of the cracks is likelyto be smaller (shorter) than the particle size of hard particles locatedin the topmost surface of the base material, and eventually drop-off ofhard particles is suppressed. The surface-coated cutting tool of thepresent disclosure can therefore have a high wear resistance and a highfracture resistance and hence a long life.

Preferably, the base material in the present embodiment has an oxygenconcentration of less than or equal to 10 at. % at a depth position of0.2 μm from the cutting edge face. In this case, extension of cracks canfurther be reduced and drop-off of hard particles can be suppressed.Accordingly, the life of the surface-coated cutting tool can further beextended. The oxygen concentration at a depth position of 0.4 μm fromthe cutting edge face and the oxygen concentration at a depth positionof 0.2 μm from the cutting edge face are desirably 0 at. %.

Strain

In the present embodiment, preferably the cutting edge face has a strainof less than or equal to 0.07. The strain in the cutting edge face canbe determined based on a base material diffraction profile of x-raydiffraction angle (2θ) and diffraction intensity based on x-raydiffractometry. The x-ray used at this time is preferablyhigh-brightness x-ray like radiation beam, since high-precisionmeasurement is possible.

Regarding a base material diffraction profile of x-ray diffraction angle(2θ) and diffraction intensity obtained by x-ray diffractometry, it isknown that the diffraction peak expands (broadens) depending on each ofcrystallite size (i.e., particle size) and strain. Each of thediffraction peak depending on crystallite size and the diffraction peakdepending on strain can be approximated by a Lorentz function to expressthe integral breadth β of the diffraction peak by the followingexpression (1), where βsize is the integral breadth of the diffractionprofile depending on crystallite size, and βstrain is the integralbreadth of the diffraction profile depending on strain.

β=βsize+βstrain tm (1)

βsize and βstrain are expressed by the following expression (2) andexpression (3) where λ is wavelength of x-ray, ε is crystallite size, θis incident angle of x-ray, η is strain (non-uniform lattice strain),and θ₀ is Bragg angle. Further, the following expressions (2) and (3)are substituted into the above expression (1) to obtain the followingexpression (4).

βsize=λ/(ε cos θ₀)   (2)

βstrain=η tan θ₀   (3)

β cos θ₀/λ=1/ε+η sin θ₀/λ  (4)

On a two-axis graph with the vertical axis representing βcosθ₀/λ and thehorizontal axis representing sin θ₀/λ, values determined from multiplediffraction profiles with different 2θ values are plotted, and the plotsare linearly regressed. The slope of the obtained regression line isstrain (non-uniform lattice strain) and the reciprocal of the segment ofthe regression line is crystallite size.

The above-described strain may be an average value. Specifically, on thecutting edge face of the base material, three given measurement sitesare determined. Respective diffraction profiles (multiple diffractionprofiles that are different in incident angle) are obtained at givendepth positions from the measurement sites, and the η value at eachmeasurement site is calculated. The average of respective η values isdetermined as the strain. The measurement sites are located in a regionof the base material at a thickness in the depth direction of 1.5 μmfrom the cutting edge face of the base material. Specifically, thestrain is measured at each measurement site as an integral value of thestrain of the base material in the region from the cutting edge face tothe 1.5 μm depth.

The inventors calculated respective η values at multiple measurementsites of the cutting edge face to confirm that there is no significantdifference between each value and the average value. Therefore, thestrain may be measured at a given single site of the cutting edge faceand the value taken at this site may be determined as the strain. If themeasured strain has an apparently abnormal value, however, such a valueshould be excluded. The single site is preferably determined in acentral portion of the cutting edge face, since the central portion ofthe cutting edge face contributes significantly to characteristics ofthe cutting tool and is therefore appropriate as a site for evaluatingthe characteristics of the cutting tool.

A sufficiently small strain of “less than or equal to 0.07” enables astill longer life of the surface-coated cutting tool. The surface-coatedcutting tool having a small strain at such a position tends to have ahigh fracture resistance. The strain is more preferably less than orequal to 0.05. In this case, a still further longer life of the cuttingtool is possible. It is most preferable that the strain is 0.

Composition of Base Material

The base material is made of a cemented carbide or a cermet. Thecemented carbide may be a WC-based cemented carbide (also including acemented carbide containing WC and Co, or alternatively a cementedcarbide containing WC and Co and additionally a carbonitride of Ti, Ta,Nb or the like). The cermet may be a cermet containing TiC, TiN, TiCN orthe like as a main component. In particular, the cermet is preferably aTiCN-based cermet. In the present embodiment, preferably the materialfor the base material has a composition intentionally containing nooxygen atoms.

Particularly when the WC-based cemented carbide is used as the basematerial, its structure may include free carbon and/or a deficient layercalled r_(l) phase or s phase, for example. Further, the surface of thebase material may be modified. For example, the base material made of acemented carbide may have a surface in which a β-free layer is formed.The base material made of a cermet may have a surface-hardened layerformed therein. The base material of which surface is modified stillexhibits desired advantageous effects.

For the base material made of a cemented carbide, the cemented carbidepreferably has a composition made up of 5 to 7 mass % of cobalt, 0.01 to3 mass % of a carbide of a first metal, and the balance of tungstencarbide and inevitable impurities. For the base material made of acermet, the cermet preferably has a composition made up of 5 to 25 mass% of cobalt or nickel, 5 to 40 mass % of tungsten carbide, and thebalance of inevitable impurities and at least one selected from acarbide of the first metal, a nitride of the first metal, and acarbonitride of the first metal. Accordingly, the base material made ofa cemented carbide or cermet particularly excellent in balance betweenhardness and strength at high temperature can be included.

The first metal is one or more kinds of metals selected from the groupconsisting of Group IV elements, Group V elements, and Group VI elementsin the periodic table. The carbide of the first metal may therefore beTiC, ZrC, VC, NbC, TaC, Cr₃C₂, Mo₂C, or the like. The nitride of thefirst metal may be TiN, TaN, or the like. The carbonitride of the firstmetal may be TiCN, ZrCN, or the like.

Particle Size of Hard Particles

In the present embodiment, preferably the base material includes hardparticles and the hard particles have a particle size of more than orequal to 0.5 μm.

The hard particles are crystal grains of a hard component among crystalgrains constituting the base material. For example, the hard particlesin the base material made of a WC-based cemented carbide are thereforeWC particles, and hard particles in the base material made of a cermetare therefore TiCN particles and particles of a composite carbonitridecontaining Ti.

The particle size of the hard particles can be measured in the followingway. First, a cross section of the base material is mirror-polished. Abackscattered electron image of a given region in the cross section isobserved with an electron microscope at a magnification of 5000×. Next,the diameter of a circumcircle of a crystal grain identified as a maincomponent of the base material (i.e., circumcircle equivalent diameter)is measured. The measured diameter is identified as the particle size ofthe hard particles. In this way, respective particle sizes of at least50 hard particles are calculated, and the average value of thecalculated particle sizes is determined as the particle size of the hardparticles.

If the particle size of the hard particles is more than or equal to 0.5μm, the length of cracks is likely to be smaller than the particle sizeof the hard particles and eventually drop-off of the hard particles issuppressed, which enables a further extended life of the surface-coatedcutting tool. If, however, the particle size of the hard particles isexcessively large, the hardness of the base material itself tends todecrease. Preferably, therefore, the particle size of the hard particlesis less than or equal to 5 μm. More preferably, the particle size of thehard particles is 0.5 to 4 μm.

As seen from the foregoing, the surface-coated cutting tool according tothe present embodiment is excellent in resistance to coating fractureincluding peel-off and chipping for example, while maintaining a highwear resistance, and therefore can have an extended life.

<<Method for Manufacturing Surface-Coated Cutting Tool>>

A method for manufacturing a surface-coated cutting tool according tothe present embodiment is a method for manufacturing the above-describedsurface-coated cutting tool. The method includes the steps of: preparinga base material precursor; preparing the base material by machining asurface of the base material precursor to form the cutting edge face;forming a coating on a base material; and performing a surface treatmenton a portion of the coating corresponding to a first region. In thisway, the surface-coated cutting tool can be manufactured having a higherresistance to coating fracture including peel-off and chipping forexample, while maintaining a high wear resistance.

Preferably the machining is one of: a first grinding process ofalternately repeating wet grinding and dry grinding; a second grindingprocess of performing low- feed low-depth-of-cut wet grinding; or athird grinding process of performing dry grinding. Further, preferablythe surface treatment includes at least brushing or blasting.

The inventors focused on machining performed on the base materialprecursor. “Base material precursor” is machined so that its surface isbeveled to form a cutting edge, to thereby form “base material.”Specifically, machining is a process performed for imparting, to thebase material precursor such as sintered material, properties suitablefor a base material of the cutting tool. In order to machine a hard basematerial precursor, wet grinding is performed industrially forsuppressing heat generation during machining or improving the processquality. The inventors found that water used for this wet grinding is asource of the aforementioned oxygen atoms. Each step is now described indetail.

<Step of Preparing Base Material Precursor>

In this step, a base material precursor is prepared. The base materialprecursor may be a cemented carbide or a cermet as described above. Theshape of the base material precursor is the one as described above andtherefore similar to the shape of the base material except that the basematerial precursor does not yet have a cutting edge face.

<Step of Producing Base Material>

In this step, the surface of the base material precursor is machined.The machining is one of a first grinding process of alternatelyrepeating wet grinding and dry grinding, a second grinding process ofperforming low-feed low-depth-of-cut wet grinding, or a third grindingprocess of performing dry grinding. In this way, the base material to beused for the surface-coated cutting tool of the present disclosure canbe produced.

The surface of the base material precursor to be machined is a ridgelinevicinity portion including a ridgeline at which a first surface and asecond surface of the base material precursor meet, and a vicinity ofthe ridgeline. The first surface and the second surface of the basematerial precursor are respective portions that are to form a rake faceand a flank face of the base material, and the ridgeline vicinityportion of the base material precursor is a portion that is to form acutting edge face of the base material.

For example, the ridgeline vicinity portion machined in an arcuate shapeforms a honed cutting edge face as shown in FIG. 4, and the ridgelinevicinity portion machined in a flat shape forms a negative-land cuttingedge face (not shown). Specifically, the machining is beveling of theridgeline vicinity portion of the base material precursor.

First Grinding Process

Examples of the wet grinding (a process using water for grinding) in thefirst grinding process may include wet brushing, wet barrel finishing,and wet blasting. Conditions for this wet grinding are not particularlylimited. For example, the wet grinding may be either high-feedhigh-depth-of-cut grinding or low-feed low-depth-of-cut grinding. Interms of the productivity, the wet grinding is preferably high-feedhigh-depth-of-cut wet grinding. Low feed and low depth of cut of the wetgrinding herein vary depending on the type of grinding. For example, inthe case of low-feed low-depth-of-cut wet brushing, the feed is lessthan or equal to 200 mm/sec and the depth of cut is less than or equalto 1.5 mm. In the case of high-feed and high-depth-of-cut wet grindingwhich is wet brushing for example, the feed is more than or equal to 300mm/sec and the depth of cut is more than or equal to 3 mm.

Examples of the dry grinding (a process using no water for grinding) inthe first grinding process may include dry brushing, dry barrelfinishing, and dry blasting. Conditions for this dry grinding are notparticularly limited. For example, the dry grinding may be eitherhigh-feed high-depth-of-cut grinding or low-feed low-depth-of-cutgrinding. In terms of the productivity, the dry grinding is preferablyhigh-feed high-depth-of-cut dry grinding. Low feed and low depth of cutof the dry grinding herein vary depending on the type of grinding. Forexample, in the case of low-feed low-depth-of-cut dry brushing, the feedis less than or equal to 150 mm/sec and the depth of cut is less than orequal to 1 mm. In the case of high-feed and high-depth-of-cut drygrinding which is dry brushing for example, the feed is more than orequal to 250 mm/sec and the depth of cut is more than or equal to 2.5mm.

The reasons why the first grinding process enables manufacture of theaforementioned cutting tool with a low oxygen concentration are asfollows. For the conventional machining of the base material precursorinto the base material, the high-feed high-depth-of-cut wet grinding isperformed. A first reason for this is a high productivity of thehigh-feed high-depth-of-cut wet grinding. A second reason for this isthat the dry grinding has been considered as causing degradation of thebase material due to heat generated during the grinding. A third reasonfor this is that the productivity of the low-feed low-depth-of-cut wetgrinding has been considered as low.

However, this high-feed high-depth-of-cut wet grinding causes oxygen toenter from the cutting edge face toward the inside of the base material,resulting in decrease of the hardness of the base material itself anddecrease of the adhesiveness between the base material and a coating.

In contrast, according to the method for manufacturing in the presentembodiment, the machining in which wet grinding and dry grinding arerepeated is performed, instead of the conventional machining in whichhigh-feed high-depth-of-cut wet grinding is performed. Such machiningprovides the treated surface (cutting edge face) with the following.

A single wet grinding process is performed to bevel the base materialprecursor while oxygen enters from the surface of the base materialprecursor. The time taken to perform this wet grinding can be shortenedas compared with the conventional process. Therefore, the width of ahigh oxygen region after the single wet grinding process is smaller thanthe conventional process. Further, the dry grinding subsequent to thewet grinding does not cause oxygen to enter into the base materialprecursor. Therefore, the dry grinding is performed for beveling whileremoving the high oxygen region formed during the preceding wetgrinding.

Thus, consequently the width of the high oxygen region is significantlysmaller than the conventional process, or there is no high oxygen regionwhich may influence the physical properties of the base material.Accordingly, the aforementioned base material having an oxygenconcentration of less than or equal to 1 at. % at a depth position of0.4 μm from the cutting edge face is produced.

Although the number of times the wet grinding and the dry grinding arerepeated is not particularly limited, each of the wet grinding and thedry grinding is performed at least once. Preferably, the wet grindingand the dry grinding are alternately repeated three or more times. Inthis way, the width of the high oxygen region formed in each wetgrinding process can further be reduced. Accordingly, the final highoxygen region width can also further be reduced. The oxygenconcentration itself in the high oxygen region can also be reduced.

Preferably, the initial process in the machining process is the wetgrinding and the final process therein is the dry grinding. Accordingly,the width of the high oxygen region formed during each wet grinding canfurther be reduced, and the final width of the high oxygen region can bemade significantly small. The oxygen concentration in the high oxygenregion can also be made low. In addition, the strain in the cutting edgeface of the base material can be controlled to be small by reducing theenergy for a single process.

Second Grinding Process

Examples of the low-feed low-depth-of-cut wet grinding in the secondgrinding process may include wet brushing, wet barrel finishing, and wetblasting, like the first grinding process. The second grinding processsuppresses entering of oxygen into the base material which is caused bythe conventional high-feed high-depth-of-cut wet grinding, and thereforeenables manufacture of the aforementioned cutting tool having a lowoxygen concentration.

The wet grinding in the second grinding process is preferably performedat certain intervals, rather than continuously. Specifically, preferablya process in which the wet grinding is performed for a given time,subsequently stopped for a given time, and subsequently performed for agiven time and so on is repeated. In this way, the advantageous effectof suppressing entering of oxygen can be improved.

Third Grinding Process

Examples of the dry grinding in the third grinding process may includedry brushing, dry barrel finishing, and dry blasting, like the firstgrinding process. Conditions for this dry grinding in the third grindingprocess are not particularly limited. For example, the dry grinding maybe either high-feed high-depth-of-cut grinding or low-feedlow-depth-of-cut grinding. In terms of the productivity, high-feedhigh-depth-of-cut dry grinding is preferable. The third grinding processsuppresses entering of oxygen into the base material which is caused bythe conventional high-feed high-depth-of-cut wet grinding, and thereforeenables manufacture of the aforementioned cutting tool having a lowoxygen concentration.

The first grinding process, the second grinding process, and the thirdgrinding process are as described above. The machining is preferably thefirst grinding process.

In this case, the cutting tool having a low oxygen concentration can bemanufactured while keeping a high productivity.

<Step of Forming Coating on Base Material>

In the present embodiment, it is suitable to form a coating on the basematerial by the chemical vapor deposition (CVD) method. The filmdeposition temperature of the CVD method is 800 to 1200° C. which ishigher than that of the physical vapor deposition method. The CVD methodcan therefore be used to produce the advantageous effect that theadhesiveness between the base material and the coating is enhanced ascompared with the physical vapor deposition method. In the coating,layers other than the aluminum oxide layer can be formed underconventionally known conditions.

When an α-Al₂O₃ layer is formed as the aluminum oxide layer, forexample, the raw material gas may for example be a gas mixture includingAlCl₃, HCl, CO₂, H₂S, and H₂, for example. Respective contents of thecomponents of the gas mixture are: 1.3 to 2.5 vol % of AlCl₃, 2 to 6 vol% of HCl, 0.6 to 6 vol % of CO₂, 0.2 to 2 vol % of H₂S, and the balanceof H₂. As to the conditions for the CVD method, the temperature is 950to 1050° C., the pressure is 1 to 10 kPa, and the gas flow rate (totalgas flow rate) is 10 to 150 L/min.

The thickness of the α-Al₂O₃ layer and respective thicknesses of otherlayers can be adjusted by adjusting the film deposition time asappropriate (the film deposition rate of each layer is about 0.5 to 2.0μm/hr).

<Step of Performing Surface Treatment on Portion Corresponding to FirstRegion of Coating>

In the present embodiment, the method includes the step of performing asurface treatment on a portion corresponding to the first region. Inparticular, the surface treatment preferably includes brushing orblasting. Accordingly, the surface-coated cutting tool canadvantageously be manufactured that can suppress sudden chipping of thecutting edge while maintaining a high wear resistance of the crystalgrains in the aluminum oxide layer.

Specifically, after the coating is formed on the base material in theabove-described manner, the surface treatment is performed on a portionof the coating, the portion corresponding to the first region. In thefollowing, an example is described in which blasting, specifically wetblasting for example is performed as the surface treatment.

As shown in FIG. 5, solid fine particles having an average particle sizeof 25 to 100 μm (e.g. ceramic abrasive grains having an average particlesize of 70 μm) are applied from the leading end of a blast nozzlearranged at an angle of 10 to 80° (e.g.) 45° to an edge ridgeline 12 ofa surface-coated cutting tool 11. Meanwhile, surface-coated cutting tool11 is rotated at 10 to 50 rpm about an axial center, i.e., a throughhole 13 at the center of the rake face.

At this time, the blasting pressure may be 0.05 to 0.25 MPa (e.g. 0.05MPa), the blasting distance may be 2 to 100 mm (e.g. 50 mm), theblasting time may be 5 to 20 seconds, and the density of the solid fineparticles may be 5 to 15 vol % (the remainder is a liquid in which wateris a main component). Because the distance from edge ridgeline 12 to theleading end of the blast nozzle varies with rotation of surface-coatedcutting tool 11, it is preferable to synchronize rotation ofsurface-coated cutting tool 11 with movement of the position of theblast nozzle so that the distance between edge ridgeline 12 and theleading end of the blast nozzle is kept constant.

The surface treatment performed on the portion of the coatingcorresponding to the first region should not be limited to theabove-described method. Widely-known conventional brushing, barrelfinishing, and various blasting treatments (sandblasting, shot peening,and the like) besides wet blasting, may be applied under knownconditions.

EXAMPLES

In the following, the present invention is described in further detailwith reference to Examples. The present invention, however, is notlimited to them.

<<Production of Surface-Coated Cutting Tool of Sample No. 1>>

The surface-coated cutting tool of Sample No. 1 (indexable insert) wasproduced in the following way. The surface-coated cutting tool of SampleNo. 1 is formed of a base material with the following specifications.

Insert Model No.: CNMG120408N-UX (manufactured by Sumitomo ElectricHardmetal)

Material: cemented carbide specified by JIS B4120 (2013)

<Production of Base Material>

First, raw material powder made up of a mixture having a composition:2.0 mass % NbC, 6 mass % Co, and the balance WC (containing inevitableimpurities) was press-formed in a predetermined shape, and thereaftersintered at 1300 to 1500° C. for 1 to 2 hours. Accordingly, a basematerial precursor was obtained.

Next, on a ridgeline vicinity portion of the base material precursor,the below-described wet grinding and dry grinding were alternatelyrepeated in this order five times. The ridgeline vicinity portion of thebase material precursor was thus machined (honed) so that an arcuatecutting edge face having a radius of 0.05 mm (R=0.05 mm) was formed. Inthis way, the base material for Sample No. 1 was produced.

Wet Grinding

-   -   type: barrel finishing    -   media: plastic    -   process liquid: water    -   time: 15 minutes

Dry Grinding

-   -   type: brushing    -   brush: nylon    -   rotational speed: 100 rpm    -   depth of cut: 0.8 mm    -   feed: 120 mm/sec    -   process liquid: none    -   time: 1 minute    -   paste: diamond paste with an average particle size of 10 μm or        less (liquid component contained in the paste is solid oil)

<Formation of Coating>

Next, a CVD apparatus was used to form a coating on the entire surfaceof the base material for Sample No. 1 under the conditions of pressure,temperature, and gas mixture composition shown in Table 1. Specifically,a TiN layer with a thickness of 0.3 μm, a TiCN layer with a thickness of8 μm, an α-Al₂O₃ layer with a thickness of 5.5 μm, and a TiN layer witha thickness of 0.7 μm were stacked in this order from the surface of thebase material to thereby produce the coating. “MT-TiCN” in Table 1 meansthat a TiCN film was formed in a relatively mild temperature environmentof 850 to 950° C. relative to other CVD methods.

TABLE 1 gas mixture composition temperature pressure coating layer (vol%) (° C.) (kPa) TiN TiCl₄: 1.0%, N₂: 40.0%, 800 7 (lowermost layer) H₂:balance TiN TiCl₄: 2.0%, N₂: 30.0%, 1000 20 (other than H₂: balancelowermost layer) MT-TiCN TiCl₄: 2.0%, N₂: 20.0%, 900 10 CH₃CN: 0.5%, H₂:balance α-Al₂O₃ AlCl₃: 2.0%, CO₂: 2.5%, H₂S: 980 6 0.7%, HCl: 5.0%, H₂:balance

<Surface Treatment>

Next, the following surface treatment (wet blasting) was performed on aportion, corresponding to the first region, of the coating formed on thesurface of the base material of Sample No. 1. Specifically, while thebase material having the coating formed on the surface of the basematerial was rotated about the through hole, as an axial center, in therake face at a rate of 60 rpm, ceramic (aluminum oxide) abrasive grainshaving a grain size of 70 μm were applied from the leading end of ablast nozzle arranged in the direction of 45° with respect to animaginary ridgeline formed by an imaginary plane including the rake faceand an imaginary plane including the flank face for performing wetblasting. At this time, the blasting pressure of the ceramic abrasivegrains was 0.10 MPa, the blasting time was 5 to 10 seconds, the densitywas 10 vol % (the remainder is a solvent in which water was a maincomponent). Further, the blasting distance from the blast nozzle to thecutting edge face on the base material was 10 mm, and the blastingdistance from the blasting nozzle to nose R on the base material was 15mm. In this way, the surface-coated cutting tool of Sample No. 1 wasproduced.

<<Production of Surface-Coated Cutting Tool of Sample No. 2>>

The surface-coated cutting tool (indexable insert) of Sample No. 2 wasproduced in the following way. The surface-coated cutting tool of SampleNo. 2 is formed of the base material with the following specifications.

Insert Model No.: CNMG120408N-UX (manufactured by Sumitomo ElectricHardmetal)

Material: cermet of grade P20

<Production of Base Material>

First, raw material powder made up of a mixture having a composition: 7mass % NbC, 7 mass % Mo₂C, 10 mass % Co, 5 mass % Ni, 20 mass % WC, andthe balance TiCN (containing inevitable impurities) was press-formed ina predetermined shape, and thereafter sintered at 1300 to 1650° C. for 1to 2 hours. Accordingly, a base material precursor was obtained. Then,machining was performed on the base material precursor under the sameconditions as Sample No. 1. Thus, the base material for Sample No. 2 wasproduced.

<Formation of Coating>

On the base material for Sample No. 2, a coating was formed under thesame conditions as those for forming the coating on the base materialfor Sample No. 1, and a surface treatment was performed on the coating.

<<Production of Surface-Coated Cutting Tools of Sample Nos. 3, 4, 5>>

The surface-coated cutting tools of Sample Nos. 3, 4, and 5 wereproduced in the same way as Sample No. 1 except that the machining forrespective base material precursors was changed, specifically exceptthat the process time and the number of repetition times of each of thewet grinding and the dry grinding were changed.

<<Production of Surface-Coated Cutting Tool of Sample No. 6>>

The surface-coated cutting tool of Sample No. 6 was produced in the sameway as Sample No. 1 except that the machining for the base materialprecursor was changed so that only the conventional wet grinding wasperformed.

<<Production of Surface-Coated Cutting Tool of Sample No. 7>>

The surface-coated cutting tool of Sample No. 7 was produced in the sameway as Sample No. 1 except that the machining for the base materialprecursor was only the conventional wet grinding and no surfacetreatment was performed on the first region of the coating formed on thesurface of the base material.

<<Production of Surface-Coated Cutting Tool of Sample No. 8>>

The surface-coated cutting tool of Sample No. 8 was produced in the sameway as Sample No. 2 except that the machining for the base materialprecursor was only the conventional wet grinding and no surfacetreatment was performed on the first region of the coating formed on thesurface of the base material.

<<Production of Surface-Coated Cutting Tool of Sample No. 9>>

The surface-coated cutting tool of Sample No. 9 was produced in the sameway as Sample No. 1 except that no surface treatment was performed onthe first region of the coating formed on the surface of the basematerial.

In this way, the surface-coated cutting tools of Sample Nos. 1 to 9 wereproduced. The surface-coated cutting tools of Sample Nos. 1 to 5 areExamples and the surface-coated cutting tools of Sample Nos. 6 to 9 areComparative Examples. For the below-described evaluation of variouscharacteristics (oxygen concentration, strain, TC(006), wear resistancetest, and fracture resistance test), five surface-coated cutting toolswere produced for each group of Sample Nos. 1 to 9.

<<Evaluation of Characteristics>><Measurement of Oxygen Concentrationand Strain>

For the surface-coated cutting tools of Sample Nos. 1 to 9, each of theoxygen concentration at a depth position of 0.4 μm from the cutting edgeface, the oxygen concentration at a depth position of 0.2 μm from thecutting edge face, and the strain in the cutting edge face (strain at adepth position of 1.5 μm from the cutting edge face) was measured in theabove-described way.

Each of the oxygen concentrations and the strain was measured at giventhree measurement sites of the cutting edge face (honed surface with R=0.05 mm), and the average value of the measurements was calculated. Oneof the three measurement sites was a central portion of the cutting edgeface. The calculated oxygen concentrations and strain (average values)are shown in Table 2.

The following apparatuses were used.

XPS analyzer (for measurement of oxygen concentration): trade name“JPS-9030” manufactured by JEOL Ltd.

x-ray apparatus (for measurement of strain): facility name “SPring-8,”Japan Synchrotron Radiation Research Institute: JASRI

Conditions for the radiation (high brightness x-ray) of SPring-8 usedfor measurement of strain by x-ray diffractometry are as follows.

beam line: BL16XU

incident x-ray energy: 10 keV

incident angle: 9.5°

scanning range: 18° to 97° at 20

In Table 2, the column “oxygen concentration at % (0.4 μm)” indicatesthe oxygen concentration (atomic %) at a depth position of 0.4 μm fromthe cutting edge face, and the column “oxygen concentration at % (0.2μm)” indicates the oxygen concentration (atomic %) at a depth positionof 0.2 μm from the cutting edge face.

<Measurement of TC(006)>

For the surface-coated cutting tools of Sample Nos. 1 to 9, an x-raydiffractometer (trade name: “SmartLab (registered trademark) 3”manufactured by Rigaku Corporation) was used to obtain a diffractionprofile of the α-Al₂O₃ layer in accordance with the θ-2θ method usingCu-Kα x-ray. The tube voltage was 45 kV and the tube current was 200 mA.As to the range of x-ray irradiation, a pinhole collimator was used toapply x-ray to a range with a diameter of 0.3 mm on the rake face.

On the surface-coated cutting tools of Sample Nos. 1 to 9, x-rayirradiation sites were defined based on imaginary edge ridgelines. Eachimaginary edge ridgeline is a line at which an imaginary extension of arake face and an imaginary extension of a flank face meet each other.Specifically, as shown in FIG. 1, measurement points (first measurementpoint 1, second measurement point 2, third measurement point 3, fourthmeasurement point 4, fifth measurement point 5) were set at 0.7 mmintervals from corner 100 along the diagonal line connecting corner 100and corner 200 of the rake face. Corners 100 and 200 are each a rakeface corner having an acute angle (θ=80°, the angle formed by imaginarytwo edge ridgelines that cross each other). To these measurement points,x-ray was applied under above-indicated conditions. From the obtaineddiffraction profile of the α-Al₂O₃ layer, TC(006) at each measurementsite was calculated. The results of the measurement are shown in Table 2below.

On the surface-coated cutting tools of Sample Nos. 1 to 9, the firstregion includes the region (region A) from the edge ridgeline to animaginary line on the rake face extending along the edge ridgeline andlocated 1 mm away from the edge ridgeline. First measurement point 1 andsecond measurement point 2 are therefore included in the first region.The second region is a region on the rake face except for the region A.Third measurement point 3, fourth measurement point 4, and fifthmeasurement point 5 are therefore included in the second region. Thus,the average value of TC(006) obtained at first measurement point 1 andsecond measurement point 2 is the value of a. The average value ofTC(006) obtained at third measurement point 3, fourth measurement point4, and fifth measurement point 5 is the value of b.

<Wear Resistance Test>

With the surface-coated cutting tools of Sample Nos. 1 to 9, cutting wasperformed under the following cutting conditions. Specifically, the time(minutes) elapsed from the start of cutting of the below-indicatedworkpiece to the time when the maximum width of an exposed portion ofthe base material exceeded 0.1 mm was evaluated. The exposed portion wasgenerated due to wear of the cutting surface during cutting. The testresults are also shown in Table 2 below. The wear resistance can beevaluated to be higher as this elapsed time is longer.

Cutting Conditions

-   -   workpiece: FC300    -   cutting speed: 500 m/min    -   feed: 0.3 mm/rev    -   depth of cut: 2.0 mm    -   cutting liquid: water-soluble cutting oil

<Fracture Resistance Test>

With the surface-coated cutting tools of Sample Nos. 1 to 9, cutting wasperformed under the following cutting conditions. Specifically, the time(minutes) elapsed from the start of cutting of the below-indicatedworkpiece to occurrence of peel-off or fracture of the coating togetherwith components adhering to the tool surface was measured. The peel-offor fracture occurs due to adhesion of the workpiece for example to thetool surface during cutting. The results are shown in Table 2. The timeelapsed before occurrence of peel-off or fracture of the coating can bemeasured to evaluate the fracture resistance of the cutting tool. Thefracture resistance can be evaluated to be higher as this elapsed timeis longer.

Cutting Conditions

-   -   workpiece: FCD450, grooved material    -   cutting speed: 200 m/min    -   feed: 0.3 mm/rev    -   depth of cut: 1.5 mm    -   cutting liquid: water-soluble cutting oil

TABLE 2 cutting performance oxygen oxygen TC(006) wear fracture concen-concen- 1st 2nd 3rd 4th 5th re- re- tration tration measure- measure-measure- measure- measure- aver- aver- sistance sistance Sample at % at% base ment ment ment ment ment age age test test No. (0.4 μm) (0.2 μm)strain material point point point point point a b b-a (min) (min) 1 0.8 8.5 0.02 cemented 7.01 7.15 7.56 7.67 7.78 7.08 7.67   0.59 12 4.5carbide 2 0.8  6.3 0.03 cermet 6.98 7.12 7.49 7.57 7.72 7.05 7.59   0.5413 4.6 3 0.7  5.3 0.06 cemented 5.49 6.47 7.01 7.74 7.86 5.98 7.54  1.56 12 6.1 carbide 4 0.9  5.4 0.09 cemented 5.49 6.47 7.01 7.74 7.865.98 7.54   1.56 12 3.6 carbide 5 0.7 11.3 0.14 cemented 5.49 6.47 7.017.74 7.86 5.98 7.54   1.56 13 3.2 carbide 6 1.2 13.2 0.08 cemented 7.017.15 7.56 7.67 7.78 7.08 7.67   0.59 10 2.5 carbide 7 1.1 14.1 0.12cemented 7.45 7.57 7.54 7.45 7.52 7.51 7.50 −0.01  9 1.6 carbide 8 1.314.2 0.32 cermet 2.64 2.54 2.52 3.12 3.21 2.59 2.95   0.36  6 1.4 9 0.8 8.5 0.02 cemented 7.45 7.57 7.54 7.45 7.52 7.51 7.50 −0.01  9 1.8carbide

<Test Results and Analysis>

As shown in Table 2, Sample Nos. 1 to 5 satisfied the relation b−a>0.5and had an oxygen concentration of less than or equal to 1 at. % at adepth position of 0.4 μm from the cutting edge face, and accordinglyprovided favorable results in both the wear resistance test and thefracture resistance test. In particular, it was found that Sample Nos. 1to 3 having sufficiently low oxygen concentration and sufficiently smallstrain had higher fracture resistance. It is seen from the foregoingthat Sample Nos. 1 to 5 were surface-coated cutting tools excellent inwear resistance and fracture resistance as compared with Sample Nos. 6to 9 failing to satisfy at least one of the relation b−a>0.5 and theaforementioned oxygen concentration.

The embodiments and Examples of the present invention are those asdescribed above. It is originally intended that features of theabove-described embodiments and Examples may be combined or modified invarious manners as appropriate.

It should be construed that the embodiments and examples disclosedherein are given by way of illustration in all respects, not by way oflimitation. It is intended that the scope of the present invention isdefined by claims, not by the description above, and encompasses allmodifications and variations equivalent in meaning and scope to theclaims.

REFERENCE SIGNS LIST

1 first measurement point; 2 second measurement point; 3 thirdmeasurement point; 4 fourth measurement point; 5 fifth measurementpoint; 10 base material; 10 a rake face; 10 b flank face; 10 c cuttingedge face; 11 surface-coated cutting tool; 12 edge ridgeline; 13 throughhole; 100 corner; 200 corner

1. A surface-coated cutting tool having a rake face and a flank face,the surface-coated cutting tool comprising a base material and a coatingformed on the base material, the base material being a cemented carbideor a cermet, the base material having a surface, the surface includingthe rake face, the flank face, and a cutting edge face connecting therake face to the flank face, the base material having an oxygenconcentration of less than or equal to 1 at. % at a depth position of0.4 μm from the cutting edge face, the coating including an aluminumoxide layer containing a plurality of aluminum oxide crystal grains, thealuminum oxide layer including: a first region made up of a region A onthe rake face and a region B on the flank face; a second region on therake face except for the region A; and a third region on the flank faceexcept for the region B, the region A being a region from an edgeridgeline to an imaginary line on the rake face, wherein the edgeridgeline is a line at which an imaginary extension of the rake face andan imaginary extension of the flank face cross each other, and theimaginary line on the rake face is a line extending along the edgeridgeline and located 1 mm away from the edge ridgeline, the region Bbeing a region from the edge ridgeline to an imaginary line on the flankface, wherein the imaginary line on the flank face is a line extendingalong the edge ridgeline and located 1 mm away from the edge ridgeline,the aluminum oxide layer satisfying a relation: b−a>0.5, where a is anaverage value of a TC(006) in the first region in texture coefficientTC(hkl), and b is an average value of the TC(006) in the second regionor the third region in texture coefficient TC(hkl).
 2. Thesurface-coated cutting tool according to claim 1, wherein the asatisfies a relation: 4<a.
 3. The surface-coated cutting tool accordingto claim 1, wherein the aluminum oxide layer is an α-Al₂O₃ layercontaining α-Al₂O₃ crystal grains as a main component.
 4. Thesurface-coated cutting tool according to claim 1, wherein the basematerial has an oxygen concentration of less than or equal to 10 at. %at a depth position of 0.2 μm from the cutting edge face.
 5. Thesurface-coated cutting tool according to claim 1, wherein the cuttingedge face has a strain of less than or equal to 0.07.
 6. Thesurface-coated cutting tool according to claim 1, wherein the cementedcarbide has a composition made up of 5 to 7 mass % of cobalt, 0.01 to 3mass % of a carbide of a first metal, and the balance of tungstencarbide and inevitable impurities, the cermet has a composition made upof 5 to 25 mass % of cobalt or nickel, 5 to 40 mass % of tungstencarbide, and the balance of inevitable impurities and at least oneselected from a carbide of the first metal, a nitride of the firstmetal, and a carbonitride of the first metal, and the first metal is atleast one kind of metal selected from the group consisting of Group IVelements, Group V elements, and Group VI elements in the periodic table.7. The surface-coated cutting tool according to claim 1, wherein thecoating further includes a compound layer made from: at least one kindof first element selected from the group consisting of Group IVelements, Group V elements, and Group VI elements in the periodic table,aluminum, and silicon; and at least one kind of second element selectedfrom the group consisting of boron, carbon, nitrogen, and oxygen.
 8. Thesurface-coated cutting tool according to claim 1, wherein the coating isa chemical vapor deposition film.
 9. A method for manufacturing asurface-coated cutting tool according to claim 1, the method comprising:preparing a base material precursor; preparing the base material bymachining a surface of the base material precursor to form the cuttingedge face; forming the coating on the base material; and performing asurface treatment on a portion of the coating, the portion correspondingto the first region.
 10. The method for manufacturing a surface-coatedcutting tool according to claim 9, wherein the machining is one of afirst grinding process of alternately repeating wet grinding and drygrinding; a second grinding process of performing low-feedlow-depth-of-cut wet grinding, or a third grinding process of performingdry grinding.
 11. The method for manufacturing a surface-coated cuttingtool according to claim 9, wherein the surface treatment includes atleast brushing or blasting.